Device and method for feeding an elastomeric yarn to a textile machine

ABSTRACT

A method and device for controlling the feed of an elastomeric yarn ( 11 ), of known elastic characteristics, withdrawn from a bobbin (B) and fed to a textile machine ( 10 ) such as a knitting machine, a stocking machine, a bobbin winder or other textile machine, the yarn possessing an intrinsic elasticity and being fed to the machine with an intrinsic speed, there being provided elements ( 18 ) for sensing the tension of the yarn ( 11 ) and elements ( 3, 12 ) for measuring and modifying this speed, both associated with a single body ( 2 ) of the device ( 1 ) and both connected to elements ( 20 ) for controlling and regulating the tension and speed parameters; elements for compensating the variation in the elongation of the yarn being provided to maintain the diameter and the quantity of the yarn fed to the textile machine constant.

The present invention relates to a device for feeding an elastomericyarn to a textile machine with the aim of obtaining an article ofconstant quality in all its parts, in accordance with the introductionto the main claim. The present invention also relates to a methodimplemented by said device in accordance with the introduction to thecorresponding independent claim.

In the textile industry, devices known as yarn feeders are usedbasically for feeding yarn to the textile machine under conditionseither of “constant quantity” or of “constant tension”.

The first are composed of mechanical members or electronic actuators,electric motors of various kind able to feed the yarn at a speedsynchronized with the operative speed of the textile machine in each ofits productive stages. In this manner the parameter relative to the“quantity of yarn” fed during the productive process is maintainedconstant in each of said operative stages, the machine hence operatingunder “constant quantity” tension feed conditions.

These devices are also used to feed an elastomeric yarn for example inlarge diameter circular knitting machines; such devices are composed ofa pulley synchronized with the main transmission shaft of the textilemachine by means of a belt, the elastomeric yarn resting on said pulleywhich by rotating enables the yarn fed to the textile machine to beunwound in a controlled manner.

Other devices of this type are for example those used to feed acontrolled quantity of elastomeric yarn during its processing within acircular textile machine for producing stockings, tights etc. Thesedevices normally use a yarn feed roller or pulley operated by electricmotors synchronized with the rotational speed of the cylinder of thetextile machine, to ensure a yarn feed of controlled or variablequantity depending on the processing stage reached.

Those devices aimed at feeding yarn “at constant quantity” do nothowever sufficiently solve the problem of feeding the elastomeric yarnin an exactly controlled quantity, because as the yarn originating fromthe spool or bobbin is “elastic” it undergoes variable elongation as afunction of the yarn unwinding tension.

To overcome these problems, other yarn feed devices known as secondgeneration devices have been developed, able to feed the yarn at“constant tension”.

These devices are composed of a yarn tension sensor connected to ameasurement and processing circuit, able to provide “closed-loop”control of a motor acting on a roller or pulley operating directly onthe yarn in order to feed it under “constant tension” feed conditions.

Such a device is known, for example, from EP950742 relating to a devicefor controlling the feed of a yarn fed to a textile machine such as aknitting machine, stocking machine or a bobbin winder; the yarnpossesses an intrinsic tension and is fed to the machine with anintrinsic speed, means being provided for sensing this tension and meansfor measuring this speed. The sensing and measuring means are bothassociated with the body of the device and are both connected to controland regulator means for said tension and speed parameters, these controland regulator means continuously measuring the values of both saidparameters during the yarn feed to the textile machine and comparing atleast one of them with a predetermined homogeneous datum in order toalso establish with precision the value of the other parameter.

This prior patent states, inter alia, that speed measurement means areassociated with motor means enabling the speed of the fed yarn to bemodified on the basis of the sensed tension value, said motor meansbeing the textile machine with which the rotary member is associated viaknown mechanical transmission members. These motor means are connectedto the control means defined by a microprocessor unit, this latter beingconnected to the textile machine control member, by which it operates onthe motor means acting on the speed measurement means.

Although these devices represent a considerable forward step with regardto the quality of the fabric or article produced by the textile machineto which they are applied, they can no longer be considered assufficient for satisfying the requirement for continuous increase in thequality of the textile article produced by elastomeric yarn. In thisrespect, although said devices feed the yarn at constant tension and arehence able to react actively to any variation in the tension of the yarnunwinding from the bobbin, they are not able to ensure an effective“constant quantity” because of the elongation of the yarn as a functionof its bobbin unwinding tension.

In this respect, such “constant tension” feed devices are able toprovide a so called “constant quantity” of yarn feed which is moreprecise the less elastic the yarn to be fed.

In contrast, an elastomeric yarn originating from a yarn bobbin which isstill full has an unwinding tension less than and hence an elongationless than an elastomeric yarn originating from a yarn bobbin which is atleast partly empty. From this is follows that if yarn is fed from two ofsuch bobbins to one and the same textile machine via two identical“constant tension” yarn feed devices, an article (formed from these twoyarns) of imperfect quality would be obtained. This is because eachyarn, even though fed at constant tension, undergoes different“treatment” by the corresponding feed device: the yarn originating fromthat bobbin which is still full would be fed at a lower speed (i.e. in asmaller quantity) than the yarn fed from the more empty bobbin in orderto compensate for the two different unwinding tensions of the yarns fromthe two bobbins. This different feed would result in an article such asthe aforesaid, in which the different yarn treatment would beidentifiable, i.e. a poor quality product would be obtained.

Another device of the aforesaid type is described in GB2162971 whichrelates to a device for feeding a yarn to a textile machine such as aknitting machine, a loom or the like. This device comprises a yarn feedmember controlled by an electric guide motor of controlled speed, saidspeed being controlled by an output signal which controls the speed ofmovement of the yarn. The speed of the guide motor is synchronized withsaid output signal, representative of the yarn feed speed. Tensioningmeans are provided to automatically maintain the yarn tension at apreselected value.

An object of the present invention is therefore to provide an improveddevice and method for feeding an elastomeric yarn to a textile machinewith the aim of obtaining an article of excellent and constant quality.

This and further objects which will be apparent to the expert of the artare attained by a device and method in accordance with the accompanyingclaims.

The present invention will be more apparent from the accompanyingdrawing, which is provided by way of non-limiting example and in which:

FIG. 1 is a front view of the device according to the invention;

FIG. 2 is a side view of a part of the device according to theinvention;

FIG. 3 is a block diagram of one embodiment of the method of theinvention; and

FIG. 4 is a flow diagram showing one stage in the method of theinvention.

With reference to said figures, and in particular to FIGS. 1 and 2,these show a device 1 for feeding an elastomeric yarn 11 at “constanttension” to a textile machine 10. This device, indicated by DTC in FIG.4, comprises a body 2 (for example box-like). With this body there areassociated a grooved wheel or pulley 3 associated with an actuator (notshown) for its movement. This actuator can be an electric motor (forexample of brushless type) associated with that face of the body 2opposite the face 6 on which the pulley 3 is present. Such a device 1 isassociated with each elastomeric yarn 11 fed to the machine, said yarnunwinding from a bobbin B and winding one or more times about the pulley3.

This pulley is directly or indirectly connected to a member 12 whichmeasures its rotation and hence the speed of this rotation. This membercan be a magnetic sensor 13 associated with the body 2 and cooperatingwith a magnet 15 associated with the pulley or a known Hall sensorassociated with the motor (brushless motor with a Hall sensorincorporated) which provides the movement of the pulley 3.

The body 2 also supports, a member 18 for measuring the tension of theyarn 11 directed to the machine 10; this member is of known type and cancomprise a usual magnetic sensor, a piezoelectric sensor, a load cell,an elastically supported armlet or another known sensor.

The tension sensing member 18, the measurement member 13 for therotational speed of the pulley and the motor connected to this latterare connected to a unit 20 for controlling and regulating the feed ofthe yarn 11 to the textile machine 10. Advantageously, this unit 20 isassociated with the device 1 (inserted into its body 2) and is able, viathe connection to said measurement members, to measure correctly andprecisely the quantity of yarn (in metres per minute) fed to themachine, using evaluation algorithms which consider both the measuredtension of the yarn 11 and the speed of rotation of the pulley. In thisrespect in determining a yarn count (expressed in DENIER or DECITEX),knowing the relationship existing between the yarn quantity in metresand the unit weight thereof, the exact weight of yarn or its quantity interms of weight fed to the textile machine (and used in the article) canbe calculated, and hence the cost of the product. To the unit 20, forexample of microprocessor type, there are connected usual settingmembers associated with the body 2; these members are an interfacekeypad 22 or usual potentiometers 23 connected to the unit. To this unitthere is also advantageously connected a display 25 on which the unit 10displays the data measured by it, such as the yarn feed speed, thequantity of yarn fed to the textile machine 10, its tension and otherdata related to the yarn or to the unit itself (programmed tension andother functions programmable by the unit, alarms, etc.).

According to the invention, between the bobbin and the device 1 there ispositioned a member 30 for compensating the variation in elongation ofthe elastomeric yarn 11, having known elastic characteristics. Thismember 30 is able to compensate the physical variation in the diameterof the yarn 11 as the diameter of the bobbin from which it unwindsdecreases, and to maintain its elongation, and hence the quantity ofyarn fed to the textile machine 10, constant.

Specifically, in the embodiment of the invention under examination, themember 30 comprises a wheel means 31 supported laterally by an actuator33, for example electrical (such as an electric motor for example ofbrushless type or similar) or air operated, which rotates it about itsaxis. This wheel means presents a groove 31A in which the yarn 11 iswound and acts as a braking member or a member for feeding the yarn tothe DTC device 1. The actuator 33 is connected (see FIG. 3) to a controlunit such as a microprocessor 34 (for example associated with said motoras in FIG. 2) connected to the unit 20 of said device. The unit 20 andthe unit 34 exchange data relative to the speed at which the yarn 11 isfed to the textile machine 10, to enable the speed of the wheel means 31to be varied so as to induce a corresponding correction to the speed ofthe yarn leaving the device 1 (via the pulley 3) and then to maintainthe speed of the yarn 11 or the quantity of said yarn fed to the machine10 constant. As shown in FIG. 3, the unit 20 can also cooperate with acontrol unit 27 for the textile machine 10.

Specifically, the wheel means 31 either brakes or feeds more yarn to thedevice 1 on the basis of a desired set yarn speed (or quantity)(indicated by SPV in FIG. 4). This setting can be in the form of:

-   -   a) the mean value of all the speeds of the yarns fed to a        multi-feeder textile machine. After this latter is activated,        the speed of each individual yarn can be measured in a few        milliseconds, hence by collaborating with the control unit 27 of        the machine 10 and measuring all the speed data of the pulleys 3        cooperating with each yarn 11 the unit 34 of each member 30 can        act on the corresponding wheel means 31 to brake the respective        yarn or to increase its feed speed to the pulley 3. As the        actuator of this latter is controlled by the corresponding unit        20, it is able to act on the yarn to decrease or increase its        speed with the aim of making that quantity thereof fed to the        textile machine 10 equal to the quantity of all the other yarns        fed to the machine and used for producing one and the same        article;    -   b) a value set for each individual yarn: in that case the units        24 and 34 interact to maintain, in the manner described under        the preceding point a), the preselected speed of the yarn 11 and        hence the desired constant quantity of yarn fed to the textile        machine 10;    -   c) a variable value depending on the processing stage of the        article. In that case the operation proceeds as under the        preceding point b).

With reference to FIG. 4, the method of the invention operates inaccordance with the following procedure: after start-up (block 40), theyarn feed speed is measured (block 41) by the DCT device 1; the speed(SPV for example equal to 50 m/min) set in the unit 34 (block 42) iscompared with the measured speed. If the yarn feed speed via the DCTdevice 1 is greater than the speed SPV, the unit 34 acts on the wheelmeans 31 to decrease the amount of yarn braking (block 43) and draw moreyarn 11 from the bobbin B so that the DCT device operates at the speedset in the unit 34 with its own pulley 3. If instead the yarn feed speedof the DCT device 1 is less than the speed SPV, the unit 34 controllingthe wheel means 31 increases the amount of braking of the yarn 11 (block44). These braking increase/decrease adjustments by the wheel means 31and consequently by the pulley 3 are repeated until the DCT device 1,which is feeding the yarn 11 at “constant tension”, has been compelledto attain a yarn feed speed equal to the speed set and programmed in theunit 34.

These adjustments hence result in a variation in the yarn tensioncontrolled by the wheel means 31 and pulley 3, the regulation of whichcauses the DCT yarn feed device 1 to balance out at a “constantquantity” yarn feed equal to the speed value SPV set in the unit 34.This method hence enables the DCT device 1 to feed an elastomeric yarnat “constant tension” and at “constant quantity”.

Obviously the speed value SPV can be varied in relation with theoperative stage achieved by the textile machine, in order to obtain avariable yarn pretension value based on the processing point.

It is also obvious that the DTC device 1 could easily accommodate themember 30 of the present invention, hence advantageously forming asingle device for yarn feed at “constant tension and quantity”.

It is likewise obvious that the yarn pre-feed actuator or wheel means 31could be of different form than that described: for example in the formof a known braking device, or a pulley or roller directly or indirectlykeyed onto the shaft of the actuator 33 to act on the pre-feed so thatmore or less yarn is fed, with the purpose of compelling the DCT device1 to feed the elastomeric yarn at “constant tension and quantity”.

The aforestated represent only some of the possible solutions; otherdifferent constructions and/or solutions will be apparent to an expertof the art on reading the aforegoing and hence lie within the scope ofprotection of the present text.

By virtue of the invention, a device for feeding an elastomeric yarn toa textile machine is obtained which acts on the yarn before it passes tothe textile machine, such that the elastic characteristics of the yarndo not influence or cannot be seen to influence the production of thearticle. In other words, the device of the invention with a member forcompensating the variation in the diameter and elongation of theelastomeric yarn before it cooperates with a known device for feedingthis yarn at constant tension and quantity. The said compensation memberacts on the yarn to brake it or to increase the speed with which it isunwound from the bobbin (i.e. by removing more yarn from the bobbin) onthe basis of a yarn withdrawal speed by said device which, in its turn,responds to a request for yarn by the textile machine. This braking oracceleration of the yarn directed to the known device for feeding theyarn at constant tension and quantity prevents said yarn being able toleave this device with variations in its physical elongation anddiameter (even if at constant tension) such as to result in theproduction of an article of imperfect appearance: in the absence of thecompensator member, said yarn when combined with another yarn ofunvaried physical characteristics would give rise to an article in whichthe different elongation and diameter of the yarns would berecognizable. This does not happen if the aforesaid compensator memberis present, this enabling the yarn to be “processed” by the feed deviceas if the yarn were without elasticity. Moreover, said member enablesthe yarn to absorb the elongation and diameter variation occurring onits withdrawal from the bobbin before entering the feed device; in otherwords, the yarn returns to its pre-stretch conditions at the moment inwhich its tension is evaluated by the DTC device.

1. A device for controlling the feed of an elastomeric yarn (11), ofknown elastic characteristics, withdrawn from a bobbin (B) and fed to atextile machine (10) such as a knitting machine, a stocking machine, abobbin winder or other textile machine, said yarn possessing anintrinsic elasticity and being fed to said machine with an intrinsicspeed, there being provided means (18) for sensing the tension of theyarn (11) and means (3, 12) for measuring and modifying this speed, saidsensing means (18) and said measuring and modifying means (3,12) beingboth connected to means (20) for controlling and regulating said tensionand speed parameters, said control and regulating means (20)continuously measuring the values of both said parameters during thefeed of the yarn (11) to the textile machine, characterised bycomprising compensator means (30) arranged to compensate the variationsin the dimensional characteristics of the elastomeric yarn (11)withdrawn from the bobbin (B) before the yarn (11) cooperates with thetension sensing means (18) and with the speed measurement means (3, 12)to enable a yarn with constant dimensional characteristics to be fed tosaid textile machine (10) for the entire duration of an articleproduction.
 2. A device as claimed in claim 1, characterised in that thecompensator means (30) comprise a member (31) in contact with the yarnand arranged to modify, if necessary, its speed of movement during itspath from the bobbin (1) to the tension sensing means (18) and speedmeasurement means (3, 12), said member being connected to actuator means(33) which enable the member (31) to act on the yarn when necessary. 3.A device as claimed in claim 2, characterised in that the member (31) isa wheel means such as a pulley or the like.
 4. A device as claimed inclaim 2, characterised in that the member (31) is a yarn braking member.5. A device as claimed in claim 2, characterised in that the actuatormeans (33) are an electric motor, an air-operated motor or the like. 6.A device as claimed in claim 5, characterised in that the member (31) isconnected to the output shaft of the electric motor defining theactuator means (33).
 7. A device as claimed in claim 2, characterised inthat the actuator means (33) are commanded and controlled by a controlunit (34) cooperating with the control means (20) for the tensionsensing means (18) and for the speed measurement and modifying means (3,12), said control means (20) exchanging information with said unit (34)relative to the speed with which the yarn (11) is fed to the textilemachine (10), to enable said control unit (34) to cause the actuatormeans (33) to act on the member (31) in contact with the yarn (11) inorder to modify the yarn speed and, vice versa, to enable said controlmeans (20) to regulate the speed of the yarn (11) fed to the textilemachine (10) on the basis of the yarn speed modification effected by thesaid member (31), said control unit (34), the actuator means (33), themember (31) controlled by said actuator means (33), the control means(20), the tension sensing means (18) and the speed measurement andmodifying means forming a control loop for the constant tension andconstant speed feed of the elastomeric yarn of the textile machine.
 8. Adevice as claimed in claim 7, characterised in that the control means(20) cooperate with means (27) for controlling the operation of thetextile machine.
 9. A device as claimed in claim 1, characterised inthat the sensing means (18) and the measurement and modifying means (3,12) are both associated with a single support defining the body (2) ofthe device (1).
 10. A method for feeding an elastomeric yarn to atextile machine such as to obtain an article of constant quality in eachof its parts, said method comprising measuring the tension and speed orquantity of the yarn (11) fed to the textile machine and unwinding froma bobbin (B), said method being characterised in that the yarn (11),after being unwound from the bobbin (B), is acted upon in such a manneras to modify its flow speed to the textile machine, said action beingeffected at a point on the path of the yarn upstream of the measurementof its speed and tension, while continuously measuring the speed of theyarn downstream of said point on the path, and acting on the yarn on thebasis of said measured speed so as to maintain a dimensional, i.e.diameter and elongation, stability of the yarn (11) fed to the textilemachine.
 11. A method as claimed in claim 9, characterised in that theaction on the yarn (11) is a braking action.
 12. A method as claimed inclaim 9, characterised in that the action on the yarn (11) is anacceleration action.